I am finding more & more countries want to see a notarized letter of consent when one parent is traveling with one or more children. This began with Mexico and Canada, and seems to be spreading. I guess they are tired of the legal hassles involved with parents abducting their kids after messy divorces.
In any case, here is a sample form that I find useful when taking my own kids while my spouse keeps the home fires warm:
http://www.familytravelforum.com/permissionletter.html